<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <button>按钮1</button>
    <button>按钮2</button>
    <button>按钮3</button>
</body>
</html>
<script>
  var buttons =document.querySelectorAll('button')
  for (let i = 0; i < buttons.length; i++) {
        buttons[i].onclick=(function (i) {
            return function () {
                console.log(i);
            }
        })(i)
  }
</script>